High-frequency electron discharge device



May 18, 1954 N. E. LiNDENBLAD HIGH-FREQUENCY ELECTRON DISCHARGE DEVICE 2Sheets-Sheet l Filed Dec. 2, 1947 mit 1 LL N lflvalnllallllalaflflallllltlllrrlfflollvrll/IfallifrfIlliniIllinillllnlllllnfllflllrlllfftrlllllnllnrllndollvfldltllll lEw A ORNEY May 18, 1954 N. E. LINDENBLADHIGH-FREQUENCY ELECTRON DISCHARGE DEVICE 2 Sheets-Sheet 2 Filed Dec. 2,1947 INVENTOR LIN DENBLAD NlLS Patented May 18, 1954 arianeiiieizritEoUnr ELEC'rRoN DISCHARGE EVIC Nils Lindenblad,A PortJefferson, Y., assigner to Radio Corporation of America, a corporationof Delaware Application Decemte 2, 1947, serial No. 789,273

23 Claims;

This invention relates to electron discharge devices and circuittherefor, especially adapted for use at very high frequencies 'of theorder of 600 megacycles ranging into many thousands of megacycles, andparticularly to an electron dis# charge device capable of operating overa Wide band of frequencies such as would be required in a radio relaysystem.

An object ofthe present invention is to provide an improved growing wave(sometimes called a traveling wave) type of tube in which a wave travelsalong a conductor arranged adjacent, parallel, and in energy couplingrelation to a stream 'of electrons.

Another object is to provide an improved electron discharge deviceamplifier capable of am*m plifying a wide band of high frequencies andwhich does not depend upon resonance 'phenomenon in the output circuit.4 l g It has been suggested in growing wave types of tubes to surroundan electron stream with a helical conductor which extends along anappreciable portion of the length of the electron stream and tosubstantially match the velocity-of the wave traveling along thishelical conductor to the Velocity of the electron stream. The helicalconductor in this case would be so constructed and arranged that itsprojected axial velocity would be different from but substantially `'ornearly equal to that of the electron stream `Vin order to assure energytransfer therebetween in the proper direction; viz, from the helicalline to the electron stream or vice versa. For a lgeneral description ofthe broad principles involved in these growing wave tubes, reference isherein made to my U. S. Patent 2,300,052, granted October' 27, 1942, andto my copending applications Serial Numbers 724,330, led January 25,1947, and 756,851, led June 25, 1947, now Patent No. 2,578,434, dated'December 11, 1951.

The growing wave tube of the present invention, in accordance with oneembodiment, achieves the desired velocity relation between the Wavetraveling vin the conductor adjacent the electron stream and theelectron stream by embedding the conductor in a suitable solid medium ofsuch dielectric and/or magnetic properties that the velocity of the wavetraveling along the embedded conductor or line has a value which assuresthe proper transfer of energy between the conductor (line) and electronstream without ceiling or spiraling the conductor. The conductor or linemay consist simply o one or a plu-'- rality of straight wires arrangedparallel to the electron stream; as for example, in thevf'orm 'of a cagearound the stream. This cage should not possess the properties of aperfect shield, such as are possessed by acylindrical-shaped electronimpermeable metallic tube. This cage form of construction of theinvention offers certain manufacturing advantages, among others.

it will be understood that one or more straight wires in 'air or vacuumwould propagate waves therealong at very vhigh velocity, approaching thevelocity ci" light. Therefore, the straight wires are embedded in asolid dielectric or magnetic medium to slow down the waves therealong topractical electron velocities.

Zt should, of course, be understood that if such dielectric and/ormagnetic material, having the required high constants for the use oflinear lines is not readily available, the use of dielectric and/ormagnetic materials with lesser constants will permit the use of coiledlines embedded therein having greater pitch than would otherwise bepossible. This means that mutual turn affects` would be reduced and thatAsuch lines could be constructed having lower characteristic impendance.

Another embodiment of growing wave tube of the invention involves theuse of a waveguide positioned adjacent and parallel to the electronstream and ll'ed with a suitable solid medium having such dielectricand/or magnetic properties that the desired velocity relation betweenelectron stream and the wave traveling through the wave guide 4isobtained. In this embodiment, however, the velocity variations whichtake place in the waveguide with changes in frequency should besuch asnot to handicap the operation of the system.

Still another embodiment of the invention utilizes a plurality of coiledbut spaced lines of very small circumference arranged parallel .to theelectron stream and lying in vacuo or embedded in a solid medium of`suitable dielectric and/or magnetic properties to obtain `the desiredwave velocity relation. The diameter of each coiled line is made sosmall that the `circunfiferenoe formed by one turn is only a smallfraction vof `a half wave. 1n this way the variable `mutual eectsVformed between adjacent turns from wave distributional effects isavoided. In other words two wave crests of equal or opposite polaritiescannot 'exist adjacent to each other inthe rcoiled line. These coiledlines may be arranged to :forni a cage.

-A more `detailed description of the invention follows in conjunctionwith fdr'awings, .Wherein':

ig. 1il1ust'rates a longitudinal crosssection 3 of the preferredembodiment of a growing wave tube constructed in accordance with theprinciples of the invention;

Fig. 2 is a transverse sectional view through the center of Fig. 1;

Fig. 3 is a detail, showing a tapered transmission line which can beconnected to the input or output end of the tube of Fig. 1;

Fig. 4 is a transverse cross-section of another growing wave tubeembodiment of the invention, using waveguides;

Fig. 5 is a longitudinal section view of the output end of the growingWave tube embodiment of Fig. 4; and

Fig. 6 illustrates a longitudinal sectional view of another embodimentof the invention which utilizes a cage formed from a plurality of smalldiameter interconnected coiled lines.

Referring to Figs. 1 and 2, the growing wave tube of the invention,which is especially suitable as an amplier of very high frequency wavesover a very wide band of frequencies, comprises a non-magnetic metallicenvelope I which surrounds a hollow cage of three Wave carrying elementsin the form of straight parallel wires I, 2 and 3, the cage, in turnsurrounding and being in energy transfer relation to an electron stream5 passing along the longitudinal axis of the tube.

The wires I, 2 and 3 are each embedded in and completely surrounded by asuitable annular solid medium 4 having dielectric and/or magneticproperties such as to produce the desired velocity relation between awave traveling down the wires and the velocity of the electron stream.The wires I, 2 and 3 are connected together at both ends of the cage bya wire ring or connecting leads 3E! and 3 I. A suitable cathode I5lbacked up with a negatively charged electron repeller electrode i6 isprovided at one end of the tube for furnishing a heavy concentratedstream of electrons which pass through the center of the cage of wiresI, 2 and 3, for the collection by a collector electrode I2 at the otherend of the end. The repeller electrode I6 is maintained at a negativepotential relative to the cathode by means of battery S. The collectorelectrode I2 is maintained at a slight positive (or if desired at aslight negative potential) relative to the cathode by means of a batteryl). The cathode is shown by way of illustration only, and in practicemay take other forms. A magnetic field coil I'I surrounds the tube andis energized by a D. C. source I8 in series with the variable resistorI9. This coil I1 is so arranged that the lines of flux produced therebyextend parallel to the longitudinal axis of the tube in order to focusthe beam of electrons along the center of the tube, and prevent theelectrons from impinging on the medium 4.

The metallic envelope I0 is at ground potential. A coaxial input line 8supplies radio frequency input current to that end of the cage of wiresI, 2, 3 which is nearest the cathode, while the amplied current isabstracted from the other end of the cage by an output coaxial line 9.In order to assure a vacuumtight shell or envelope Il), glass beads 22and 23 are provided in the input and output coaxial lines at a locationnear shell I0. Other glass beads 20, 2| and 24 are also provided atthose locations where leads enter the interior of the envelope I0.

The cage of wires I, 2 and 3 has a length which is a plurality ofwavelengths long, for example 15 to 40 wavelengths long at the meanoperating frequency, and Aprovides a velocity for waves d traveling overthe wires which is determined by' the dielectric and/or magneticmaterial in which they are embedded. If desired, the wires I, 2 and 3may be given such D. C. potentials as may be required by particularcircuit designs.

If a predominantly dielectric medium 4 is employed, it is necessary, inorder that conventional electron accelerating voltages may be used, forthe material to have a high dielectric constant. One such material whichmay be used is titanium dioxide. If a predominantly magnetic medium isemployed for material 4, this medium may comprise extremely ne powder ofa suitable iron alloy or a powder comprising an iron oxide. This powdershould be dispersed in and bound together by a suitable dielectricbinder preferably one that can be molded. Suitable proportions ofdielectric and magnetic materials may be used in a mixture to obtain amedium which will give a desired propagation velocity for the wavestraveling along the embedded wires I, 2 and 3.

Because the characteristic impedance of the cage I, 2, 3 is diiferentfrom that of the coaxial input and output R. F. lines 8 and 9, it isnecessary to match the impedance of these coaxial lines to thecharacteristic impedance of the cage. Where the cage has a .highercharacteristic impedance than the coaxial lines, it may be advisable toinsert a tapering impedance X as a transmission line link or impedancetransformer between the coaxial lines and the terminals of the cage.This link X is inserted externally of the electron discharge devicebetween the cage terminal and the coaxial line, as shown. It should benoted that the diameter of the tapering link X decreases from a pointnear the cage to the point where the link joins the coaxial lines 8 or9. These coaxial lines may have an impedance 0f 50 ohms, for example,while the cage may have a considerably higher characteristic impedance.Where the reverse conditions exist, that is, where the cage has acharacteristic impedance less than that of the coaxial lines, then theremay be used a tapering impedance transmission line link or impedancetransformer 25 as shown in Fig. 3, where the diameter of the link 25increases from a point near the cage to the point where the link joinsthe coaxial input or output line.

If the medium 4 is predominantly magnetic, the cage of wires I, 2, 3 isapt to possess a high characteristic impedance Zo. If the medium 4 ispredominantly dielectric, then the cage of wires I, 2, 3 is apt topossess a low characteristic impedance Zo.

Fig. i shows a construction of growing wave tube in which a piurality ofwave carrying elements in the form of similar and coextensive waveguidesA, B, C and D are symmetrically arranged around the longitudinallyprojected electron stream ti. Each Wave guide comprises a metalenclosure having a slot ll extending down the length thereof. This slotis arranged parallel to and in proximity to the electron stream 5. Eachwaveguide is lled with a suitable solid medium 4', possessing dielectricor magnetic properties or a mixture of both, as outlined above inconnection with medium 4 of Figs. l and 2. The wave velocity along thewaveguides A, B, C and D in air or vacuum, Without the solid medium,would be relatively high as compared to practical electron velocities.At both ends of the tube, the slots in the waveguides are bridged bywire connections 33, 34, 35 and 35. The. wire connections Stato 36 arerespectively andere connected at com ends of4 the waveguides to wirerings 5t by means of leads 5l, 52, 53 and 54. The input coaxial line,not shown, supplies radio frequency current to the ring 50 at the end ofthe tube nearest the cathode (not shown), While the amplified Outputcurrents are taken ofi from the ring' 5U at that end of the tube nearestthe collector iii, and' supplied to the R. F. output coaxial line 56(note Fig. 5). A metallic cover or shield 55 is provided atl the outputend of the tube, and a similar shield may be provided at the input endofthe tube. y

Although three embedded wires i 2 and 3 have been shown for the cage ofFigs. 1 and 2, and four waveguides A, B, C and D have been shown for thetubes of Figs. 'l and 5, it should be understood that these are"r onlyfor purpose or illustration and that fewer or agreater number of theseele` ments may be en'iployedV in practicing the invention. EvenV asingle embedded wire or a single .vaveguide may be used in the tube ofthe invenA- tion.

Fig. 6 illustrates another embodiment of the invention employing a cagecomposed of` a plurality of wave carrying. elements in the form ofcoiled lines ell each ofY which has relatively large pitch and adiameter so small that the circumference formed by one turn is only asmall frac` tion of 'a half Wave of `the operating radio frequen'cyenergy. The ends of the coiled lines are f connectedV together as shown,in a manner somewhat similar to that shown in Fig. l, in order to form acage. Although only two such lines are shown, in practice, three or moresuch lines may be used, .properly spaced apart.v The coiled lines may beembedded in and completely surrounded by a suitable solid material e!having desired dielectric and/or magnetic properties, or used in vacuomerely by arranging them within the evacuated envelope Il) suitablyspacedirom electron stream projected by the cathodetoward the collectorelectrode. It will be understood that Where the coiled lines el] areembedded in a wave retarding solid medium the pitch'of the helix can bemade as great ask desired; In Fig. 6, the electron beam will pass downthe center of the cage and be internal relative to the* coiled lines. Iidesired, the electron beam can be a hollow stream passing adjacent tobut eX`- ternal of the cage. Only the essential come ponente of thetraveling wavetube have been shown diagrammatically inlFig. 6, in ordernot to unnecessarily complicate the drawing. The input radio frequencymeans and the output radio frequency means may comprise coaxial linesconnected to .the cage inthe same manner as shown in Fig. 1.

The arrangements of the cage of Figs. l, 2 and 6, and of the waveguidesof Figs. l and 5 are such thatthe input waves travel longitudinally downthe cage or waveguides at the portion of the tube nearest the cathodeata velocity slightly greater` than the velocity ofthe electron streamin order to impart energy to the electrons and bunch them, while thisvelocity relation is reversed along the central portion and opposite endof the tube in order to abstract energy from the stream.

It should be understood that the line elements" 6 cage have identicaldimensions and cha'ractei"e istics'.

What is claimed is:

l. An electron discharge device including means for projecting a streamof charged particles, a radio frequency wave carrying element positionedparallel to the path of said stream and adapted to be in energy couplingrelation to said stream, said element being embedded in a solid mediumhaving a dielectric constant caus-A ing the velocity of the wavestraveling along the length of said element to match approximately thevelocity ci said stream of charged particles, said element beingcompletely surrounded by said" medium.

2. An electron discharge device including means for .projecting a streamof charged particles, a radio frequency wave carrying element positionedparallel to the path of said 'stream and adapted to be in energycoupling relation' to said stream, said `element being embedded in asolid medium having dielectric and magnetic properties causing thevelocity of the waves traveling along the length of said element`A tomatch approximately the velocity of said stream ci' charged particles,said element being come pletely surrounded by said medium. y

3. An electron discharge device including means for projecting a streamof charged pare ticles, a conductor positioned parallel to the path ofsaid stream and adapted to bein energy couepiing relation to saidstream, said conductr bee em edd-.ed in a solid medium having a highdielectric constant to reduce the velocity of waves traveling along saidconductor, said conductor being completely surrounded by said medium,means for producing a magneticeld having nur; lines'running parallel tosaid stream of charged particles, and a radio frequency terminal meanscoupled to said conductornear one end thereof.

Il. An electron discharge device including means for projecting a streamof charged par? ticles, a straight conductor positioned parallel to thepath of said stream and adapted to be in energy coupling relation tosaid stream, said conductor being embedded in a solid Amediun'fihaving ahigh dielectric constant to reduce the velocity of Waves traveling alongsaid conductor, said conductor being completely surrounded b y saidmedium, means for producing a magnetic field having flux lines runningparallel to said stream of charged particles, and a radio frequencyterminal means coupled to said conductor near one end. thereof.

5. An electron discharge device including means for projecting a streamof chargedpare ticles, astraight conductor positioned parallel to thepath of said stream and adapted to be in energy coupling relation tosaid stream, said coiiductor being embedded in a solid medium having ahigh dielectric constant to reduce the velocity of waves traveling alongsaid conductor, said conductor being completely surrounded by saidmedium, a radio frequency input terminal means coupled to one end ofsaidconductor, and a radio frequency output terminal means coupled tothe other end of said conductor.

G. An electron discharge device including means for projecting a streamof charged particles along an axis of'saidrlevice, a plurality o'lstraight conductors spaced from one another and positioned parallel tothe path 0I" said stream and forming a cage around said stream, meansfor producinglines of vmagnetic luxin' a direction parallel to thepathof -saidstieam for causing said stream to travel along said axis, saidconductors being embedded in a solid medium hav-v ing a high dielectricconstant to reduce the velocity of waves travelingY along saidconductors, at least a portion of said medium being outside said cage,connections between said conductois at both ends thereof, a radiofrequency input terminal means coupled to that end of said con ductorsnearest the source of charged particles, and a radio frequency outputterminal means coupled to the other end of said conductors.

7. An electron discharge device including means for projecting a streamof charged par ticles, a plurality of straight conductors spaced fromone another and symmetrically disposed to form a cage around the path ofsaid stream and arranged parallel to the path of said stream, saidconductors being adapted to be in energy transfer relation to saidstream by virtue of the space therebetween, a hollow annulus of solidmaterial surrounding said stream and embedding said conductors therein,said annulus having dielectric and magnetic properties causing a wavetraveling along said conductors to have a velocity which approximatesthe velocity of said stream of charged particles, at least a portion ofsaid medium being outside said cage, means for focussing said stream tofollow a path parallel to the lengths of said conductors, connectionsbetween said conductors at both ends of said annulus, and 2 input andoutput radio frequency terminal means coupled to opposite ends of saidconductors.

8. An electron discharge device including with in an evacuated envelopemeans for projecting a stream of electrons along an axis of said device,a plurality of coextensive and similar straight waveguides extendingparallel to but spaced from said axis and forming a cage around saidstream, each of said waveguides having a slot adjacent said stream andextending along the length of said guide, said guides having in theirinteriors a solid medium having dielectric and magnetic propertiescausing the velocity of the waves traveling along the guides toapproximate the velocity of said stream, connections between said guidesat both ends thereof, a radio frequency input terminal means coupled tosaid connections at that end nearest the source of electrons, and aradio frequency output terminal means coupled to said connections at theother end thereof.

9. An electron discharge device as defined in claim 1, characterized inthis, that said element is a coiled line of relatively large pitch.

10. An electron discharge device including means for projecting a streamof charged particles, a plurality of physically spaced wave carryingelements positioned parallel to the path of said stream and forming acage around said stream, said elements being embedded in a solid mediumhaving dielectric properties causing the velocity of waves travelingalong said elements to approximate the velocity of said stream,electrical connections between correspondingly positioned ends of saidelements, a radio frequency input terminal means coupled to theconnections at one end of said elements, and an output terminal meanscoupled to the connections at the other end of said elements, each ofsaid elements comprising a coiled line whose pitch is relatively' largeand Whose diameter is so small that the circumference formed by one turnis only a small fraction of a half wave of the operating frequency.

11. An electron discharge device according to claim 2 wherein themagnetic properties of said medium predominate over the dielectricproperties.

12. An electron discharge device including means for projecting a streamof charged particles, a radio frequency Wave carrying element positionedparallel to the path of said stream and adapted to be in energy couplingrelation to said stream, said element being embedded in a soliddielectric material having dispersed therein comminuted particles ofmagnetic material, the properties of said dielectric material andparticles of magnetic material causing the velocity of the wavestraveling along the length of said element to match approximately thevelocity of the stream of charged particles, said element beingcompletely surrounded by said medium.

13. An electron discharge device including means for projecting a streamof charged particles, a plurality of radio frequency wave carryingelements spaced from one another and positioned parallel to the path ofsaid stream and forming a cage around said stream, said elements beingembedded in a solid medium comprising powdered magnetic material whosecharacteristics cause the velocity of the waves traveling along thelength of said elements to match approximately the velocity of thestream of charged particles.

14. An electron discharge device including a plurality of spaced,parallel radio-frequency wave-carrying elements forming a cage, meansfor reducing the velocity of waves traveling along said elements to apredetermined wave velocity comprising a solid dielectric medium inwhich said elements are embedded, and means for projecting a stream ofcharged particles coaxially of said cage and parallel to said elementsat a velocity approximately matching said predetermined wave velocity.

15. An electron discharge device including means for projecting a streamof charged particles, a plurality of spaced wave carrying elementspositioned parallel to the path of said stream and forming a cage aroundsaid stream, said elements being embedded in a solid medium havingdielectric properties causing the velocity of waves traveling along saidelements to approximate the velocity of said stream, connections betweencorrespondingly positioned ends of said elements, a radio frequencyinput terminal means coupled to the connections at one end of saidelements, and an output terminal means coupled to the connections at theother end of said elements.

16. A traveling wave tube including a radio frequency wave carrying linehaving a structure determining a relatively high in vacuo wave velocitytherealong, means for reducing the velocity of Waves along said line toa substantially lower wave velocity than said in vacuo velocitycomprising a solid medium in which said line is embedded, said linebeing completely surrounded by said medium, means for projecting astream of electrons parallel to and in energy-coupling relation to saidline at a velocity substantially matching said lower wave velocity, andinput and output transmission lines coupled to the input and outputends, respectively, of said iirst named line.

17. A traveling wave tube as in claim 16, wherein said medium ispredominantly dielectric.

18. A traveling wave tube as in claim 16, wherein said medium ispredominantly magnetic.

19. A traveling wave tube as in claim 16,

9 wherein said first named line comprises a straight Wire.

20. A traveling wave tube as in claim 16, wherein said rst named linecomprises a coiled line of relatively large pitch.

21. A traveling wave tube as in claim 16, wherein said first named linecomprises a plurality of elongated conductors parallel to and forming acage about said stream.

22. An electron discharge device including means for projecting a streamof charged particles along an axis of said device, a plurality of Wavecarrying elements extending parallel to but spaced from said axis andforming a cage around said stream, and means. causing the velocity ofwaves traveling along said elements to approximate the Velocity of saidstream comprising a solid medium adjacent to at least a portion of thesurface of each of said elements.

23. An electron discharge device as defined in claim 22, furtherincluding connections between said elements at both ends thereof, aradio fre- 10 quency input terminal means coupled to said connections atthat end nearest the source of charged particles, and a radio frequencyoutput terminal means coupled to said connections at the other endthereof.

References Cited in the le of this patent UNITED STATES PATENTS NumberName Date 2,064,469 Haeff Dec. l5, 1936 2,197,123 King Apr. 16, 19402,300,052 Lindenblad Oct. 27, 1942 2,304,540 Gassen Dec. 8, 19422,367,295 Llewellyn Jan. 16, 1945 2,412,805 Ford Dec. 17, 1946 2,508,479Wheeler May 23, 1950 2,541,843 Tiley Feb. 13, 1951 2,575,383 Field Nov.20, 1951 FOREIGN PATENTS Number Country Date 508,354 Great Britain June29, 1939

